Method for thermal transformation of biomass

ABSTRACT

In the method for thermal biomass processing, comprising charging the material in a converter, pyrolyzing said material at a temperature ranging between 650 and 950° C. in the medium of a reducing gas, feeding of steam after the pyrolysis reaction has been completed, and isolating the resultant solid residue, reducing gas is prepared by combusting a hydrocarbon fuel at an air consumption factor α ranging from 0.85 to 1.1, and by mixing the resultant combustion products together with the biomass pyrolysis gases, the ratio between said gases and said combustion products being (1-3):1.  
     The proposed method for biomass processing makes possible using a biomass as a pollution-free fuel, as well as for simultaneously producing activated charcoal having high specific surface area ranging from 280 to 500 ml/100 g.

TECHNICAL FIELD

[0001] The present invention relates generally to thermal pyrolysis; more specifically it concerns a method for thermal biomass processing.

BACKGROUND ART

[0002] Known in the present state of the art is a method for thermal processing of vegetable origin materials comprising preparing charcoal resulting from pyrolysis (cf. RF Pat. No 2,039,078 A).

[0003] However, the method in question suffers from too high a power consumption rate due to heat transfer through the wall, a long-time pyrolysis reaction, and a low charcoal adsorption activity (40-50 ml/100 g).

[0004] Another method for thermal processing of vegetable-origin materials is known to comprise loading the material, its pyrolysis, and discharging the solid residue (i.e., charcoal) (cf. USSR Patent No 1,808,003 A).

[0005] However, the method also suffers from too high a power consumption rate of the process (steam-to-bone-dry wood ratio being (0.6-1.6):1 at 400 to 800° C.), and a low absorbing activity of the resultant charcoal (40 to 50 ml/100 g).

[0006] A method for thermal processing of a biomass is also known, said method being conducting at 650 to 950° C. in the medium of a reducing gas resulting from combusting a hydrocarbon fuel at an air consumption factor α of from 0.4 to 0.85) (cf. RF Pat. No 2,124,547 A).

[0007] However, the method also suffers from a high power consumption rate and inadequately high activity of the resultant charcoal (not over 250 ml/100 g).

DISCLOSURE OF THE INVENTION

[0008] It is a principal object of the present invention to provide a method for thermal processing of a biomass, capable of reducing power consumption rate thereof and enhancing adsorption activity of the resultant charcoal.

[0009] Said object is accomplished due to the fact that in a method for thermal processing of a biomass, comprising loading the material in a converter, pyrolyzing said material at a temperature ranging between 650 and 950° C. in the medium of a reducing gas, feeding of steam after the pyrolysis reaction has been completed, and isolating the solid residue, said reducing gas being prepared by combusting a hydrocarbon fuel at an air consumption factor α ranging from 0.85 to 1.1, and mixing the resultant combustion products together with the biomass pyrolysis gases, the ratio between said gases and said combustion products being (1-3):1.

[0010] Said object is accomplished also due to the fact that once the pyrolysis reaction has been completed, saturated steam is fed at a temperature ranging from 105 and 140° C. and a weight percentage ratio between said saturated steam and the material under processing equal to (0.1-0.25):1.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In what follows the present invention is explained in the disclosure of an exemplary embodiment thereof given by way of illustration to be taken in conjunction with the accompanying drawing representing a flowsheet diagram of the method for thermal processing of a biomass, according to the present invention.

[0012] Best Method of Carrying Out the Invention

[0013] It is common knowledge that the principal reagents of the reducing gas are H₂, CO, CO₂, H₂O, CH₄, C₂H₄, C_(n)H_(m) and hence the rate of the pyrolysis reaction depends (at the same temperature) on the volume concentration of said gas components. The composition of the reducing gas may be changed depending on the air consumption factor involved in combusting a hydrocarbon fuel, the higher said factor the higher heat evolution and the content of H₂O and CO₂ in the fuel combustion products. It has been established by the inventors, the biomass pyrolysis gases emerging from the converter at 220-350° C., contain the same components as the combustion gases (with the factor a of from 0.85 to 1.1) fed from the generator for the biomass pyrolysis. Merging the flows of the combustion products with the pyrolysis gases results in heat recovery to the process and increased concentration of the reagents indispensable for the biomass pyrolysis reaction, namely, H₂O, CO, CO₂, H₂, CH₄. It is due to recycling the pyrolysis gases into the process that the power consumption rate of the process is much reduced.

[0014] The limit weight ratio of the pyrolysis gases and the fuel combustion products, viz, (1-3):1 has been found experimentally upon processing the various vegetable-origin materials, the lower limit being conditioned by providing the highest pyrolysis temperatures, and the upper limit, by providing the lowest temperatures.

[0015] The fact that completing the pyrolysis reaction is followed by feeding saturated steam at a ratio of (0.1-0.25):1 makes it possible to cool the activated charcoal and enhance adsorption activity thereof (i.e., the iodine value and optical transmission of the toluene extract). Feeding saturated steam at a ratio below 0.1:1 fails to considerably increase the iodine value, whereas with the steam feeding ratio above 0.25:1 the iodine value is increased but the yield of activated charcoal is badly affected. When preparing activated charcoal it is expedient that saturated steam has a temperature of from 105 to 140° C. Use of saturated steam makes possible removing the remainder of the hydrocarbon residues disposed on the charcoal surface in order to prepare charcoal having a 99.7 to 100-percent optical transmission of the toluene extract.

[0016] The appended Drawing represents a flowsheet diagram of the method for thermal processing of a biomass. Shown in the diagram are: converter 1, generator 2, mixer 3, cooled bin 4, air blower 5, and gas blower 6. Arrow A indicates the direction of charging the biomass, arrow B, the direction of steam feeding, arrow C, the direction of discharge of the solid residue, and arrow D, the direction of feed of pyrolysis gases to the boiler.

[0017] The method is carried into effect as follows. The pre-dried biomass is continuously charged from a feed hopper (not shown) through an air-tight feeder into the converter 1 appearing as a metal housing lined from inside with a refractory material resistant to a reducing medium. A reducing gas is fed in a counterflow to the material through a branchpipe and a system of openings (not shown). The reducing gas is prepared b mixing the combustion products arriving from the generator 2, and the biomass pyrolysis gases picked off by the gas blower 6 from the converter 1 at a temperature of 230-350° C., and fed to the mixer 3. The remainder pyrolysis gases are fed for combustion in heat-generating apparatus (e.g., such as boilers). Saturated steam is fed at 105-140° C. to the converter 1 downstream along the direction of feed of the material to withdraw a majority of the heat from activated charcoal and at the same time cleans its surface from the remainder hydrocarbons. Then the cooled activated charcoal is from the lower portion of the converter 1 to the bin 4 cooled by the air blower 5, wherefrom the heated air is fed to the generator 2 for fuel combustion. The resultant activated charcoal has a specific surface area (with respect to iodine) ranging from 280 to 500 ml/100 g and a density of from 140 to 180 kg/m³.

EXAMPLE

[0018] Waste products of the wood-working industry first are divided to a particle size of from 15 to 35 mm, then dried and heated by a reducing gas prepared by intermixing the products of combusting a hydrocarbon fuel in the generator at a factor a equal to 0.8, and the pyrolysis gases, the ratio between said gases and the combustion products being 2.8:1. The time of the pyrolysis reaction is 25 min. Saturated steam having a temperature of 110° C. is fed to the lower portion of the converter 1, the ratio between the steam and the material being processed being 0.1:1. The yield of activated charcoal is 24.8%, a specific surface area (with respect to iodine) equals 286 ml/100 g, optical transmission of the toluene extract, 99.7%, and charcoal density, 173 kg/m³. The remainder of the pyrolysis gases are fed by the gas blower to the boiler furnace to be combusted there together with an additional amount of fuel fed thereto. The smoke fumes are free from 3-4-benzopyrene and carbon monoxide, the content of nitrogen oxides thereof being 34 mg/m³.

[0019] The herein-proposed method for biomass processing makes possible using a biomass as a pollution-free fuel, as well as for simultaneous production of activated charcoal having high specific surface area.

Industrial Applicability

[0020] The present invention can find application in the forestry engineering industry for salvage of wood waste products, as well as in farming practice for salvage, in particular, straw, stalks and cops of maize and helianthus, and also husks of millet, rice, cotton, and the like, 

1. A method for thermal biomass processing, comprising charging the material in a converter, pyrolyzing said material at a temperature ranging between 650 and 950° C. in the medium of a reducing gas, feeding of steam after the pyrolysis reaction has been completed, and isolating the resultant solid residue, CHARACTERIZED in that said reducing gas is prepared by combusting a hydrocarbon fuel at an air consumption factor a ranging from 0.85 to 1.1, and by mixing the resultant combustion products together with the biomass pyrolysis gases, the ratio between said gases and said combustion products being (1-3):1.
 2. The method of claim 1, CHARACTERIZED in that saturated steam is fed at a temperature ranging from 105 and 140° C., and a weight percentage ratio between said saturated steam and the material being processed is equal to (0.1-0.25):1. 